Improved air-laydown apparatus for producing webs for nonwoven fabric

ABSTRACT

Apparatus is disclosed which is suitable for high speed production of uniform, lightweight webs by air-laydown of textile fibers. A toothed disperser roll projects the fibers into an airstream of high uniform velocity and low turbulence to form a thin fiber stream from which the fibers are deposited in web form on a moving screen. Air-flow control means adjacent the screen causes the depositing fiber stream to shift back and forth rapidly to eliminate web streaks.

I United States Patent 11 1 Miller 1 1 Oct.31l,l973

[ IMPROVED AIR-LAYDOWN APPARATUS FOR PRODUCING WEBS FOR NONWOVEN FABRIC[75] Inventor: Donald Miller, Newark, Del.

[73] Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

[22] Filed: June 14, I971 [21] Appl. No.: 152,725

52 us. c1. 19/1563 51 1m. (:1 ..D01g 25/00 [58] Field of Search 19/84,89, 155, 156-1564,

[56] References Cited UNITED STATES PATENTS 2,103,769 12/1937 Drill19/155 FOREIGN PATENTS OR APPLICATIONS 93,843 4/1960 Netherlands 19/155709,612 5/1954 Great Britain.... 19/163 1,050,832 12/1966 GreatBritain.... 19/1564 Primary Examiner-Dorsey Newton Attorney-Norris E.Ruckman 57 ABSTRACT Apparatus is disclosed which is suitable for highspeed production of uniform, lightweight webs by airlaydown of textilefibers. A toothed disperser roll projects the fibers into an airstreamof high uniform velocity and low turbulence to form a thin fiber streamfrom which the fibers are deposited in web form on a moving screen.Air-flow control means adjacent the screen causes the depositing fiberstream to shift back and forth rapidly to eliminate web streaks.

2 Claims, 6 Drawing Figures Pmmlinncrao ms Sm W 2 3.768.120

34 INVENTOR DONALD F. MILLER BY mzm ATTORNEY PAIENIEDnmso ms 3,768,120

INVENTOR DONALD F. MILLER ATTORNEY IMPROVED AIR-LAYDOWN APPARATUS FORPRODUCING'WEBS FOR NONWOVEN FABRIC BACKGROUND OF THE INVENTION Thisinvention relates to an air-laydown apparatus for assembling textilefibers into webs and is more particularly concerned with improvements incollecting textile fibers to form webs which are suitable for use inproducing high quality nonwoven fabric.

Nonwoven fabrics are produced from fibrous webs by bonding orinterlocking the fibers to provide durability and strength. The fibersof the web may be hydraulically entangled by treatment with high energyliquid streams as disclosed in Evans U.S. Pat. No. 3,485,706, issuedDec. 23, 1969. When producing relatively heavy weight textile fabricLauterbach U.S. Pat. No. 2,910,763, issued Nov. 3, 1959, discloses thatfiber interlocking may be initiated by treatment with a needle loom andcompleted by crimping or shrinkng the fibers. Production of bondednonwoven fabrics may be accomplished as disclosed in Graham U.S. Pat.No. 2,765,247, issued Oct. 2, 1956. The quality of fabric produced bythese methods depends upon the 'quality and uniformity of the web whichis treated.

Webs suitable for producing high quality nonwoven fabrics, by treatmentsof the above type, can be prepared by air laydown of textilefibers.Priorart airlaydown processes and apparatusare illustrated by BureshU.S. Pat. No. 2,451,915, issued Oct. 19, 1948, Plummer et a1. U.S. Pat.No. 2,676,363, issued Apr. 27, 1954, and Owens et a1. U.S. Pat. No.3,481,005, issued Dec. 2, 1969. Staple fibers are shipped as a compactedmass. Conventional picking and carding operations are used to separatethe fibers. The. resulting loosely opened fiber lap is fed to a tootheddisperser roll and a stream of air is sucked or blown over the roll. Theroll is rotated at high speed to feed the fibers into the air stream,the objective being to feed individual fibers rather'than clumpsor-groups of fibers. The fibers are carried by the air stream through aduct to the screen surface of a condenser roll or conveyor, where thefibers are deposited over a-relatively large surface area to form alayer on the moving screen.

It has been found that it is necessary to control the turbulence in theair stream in order to produce uniform, non-blotchy, lightweight webs(e.g., of 3 ounces per square yard or less) at rates greater than about2 pounds per inch of disperser-roll width per hour (lb./in.hr.). At lowturbulence levels, variationsin the air stream to the disperser-rolland/or density variations in the fiber lap can cause streaks in themachinedirection of the web. At higher turbulence levels thesevariations are blended and do not appear in the web, but the blotchlevel (small-scale fiber clumping) increases with turbulence.

SUMMARY OF THE INVENTION The present invention is an improvement inairlaydown apparatus of the type having duct means for conveying fibersin a controlled flow of air, fiber disperser means for projecting fibersinto the duct means to form a thin stream of fibers in air, air supplymeans for directing a low turbulence flow of air through the duct means,and condenser means for collecting the fibers on a moving screen to forma web. The improvement is in providing air-flow control means nearopposite edges of the screen for shifting the fiber stream rapforalternately interrupting air flow on opposite sides of the fiber streamsat a frequency of at least 25 cycles per minute for each yard per minuteof screen travel.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic longitudinalvertical section of a form of air-laydown machineto illustrate use ofone embodiment of this invention.

FIG. 2 is a fragmentary enlarged longitudinal vertical section of thefiber condensing section of the above machine showing an embodiment ofthis invention.

FIG. 3 is a fragmentary section taken along the line 33 of FIG. 2.

FIG. 4 is a fragmentary enlarged section of FIG. 3.

FIG. 5 is a diagrammatic fragmentary plan view of another embodiment ofthis invention.

- FIG. 6 is a diagrammatic fragmentary plan view of another embodimentof this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now toFIGJl,there isshown a fiber feeding means consisting, in this embodiment, of aconveyor belt 2, feed roll 3, compressing roll 4 and shoe 5 forsupplying fiber 1 to the disperser roll 8. The disperser roll separatesthe fibers and carries them mixed with the air adjacent to the rollsurface through the space between the roll and disperser plate 10, anddischarges this mixture centrifugally into duct 20. A shroud or casing 9extendsaround the disperser roll from the lower edge of doff-bar 12 tofeed-roll 3. The fibers projected from the disperser roll form a thinfiber stream 22 in air flowing through the duct and are then separatedfromthe air as web 24 on condenser screen 26.

Air is supplied from air passage 14, which haslarger cross-sectionaldimensions than the duct 20. The parallel walls 16 of air passage areconnected to the duct walls 20 by converging section 18 of the flownozzle configuration. Screens 38 and 42, and honeycomb structure 40,provide a uniform flow substantially free of turbulence and vorticity.Air is blown into the air passage by one or more fans 36, through a ductsystem 33, shown diagrammatically.

The fibers are deposited to form a web on continuous, moving screen 26which is driven and supported by rolls 28 and 30. The air flows throughthe screen and is withdrawnthrough vacuum duct 34. Part of the airpasses through air-flow valve 13'. The air may be filtered to remove anyparticles passing screen 26 and then be recirculated to fan 36. Severalfans in series or an open air system with one or more fans supplying theK airand one or more fans exhausting the air can also be used. Thescreen 26 is sealed against the fiber duct 20 and the vacuum duct 34 bysealing means 32 such as a plate of polyethylene.

FIGS. 2, 3 and 4 show air-flow valves 13 and 13, as preferredembodiments of the air-flow control means, in greater detail.

The valves shown comprise drums 23 and 23, each with two opposedopenings 15 and each of which approximates the area of the closed area17. Drums with four or eight openings can be used. The valves arelocated just behind the condenser screen 26 with appropriate seals 19.The two valves are synchronized so that when valve IB kQAhe right-handedge of the fiber condensing area is fully open the other valve 13 isfully closed. This results in the fiber stream being shifted to theright and then to the left as the valves are turned.

As shown the two valves are mounted on a common shaft 21 driven by motor25. The two valves could be mounted on separate shafts and driven bysynchronized motors.

FIG. 5 shows the use of two oscillating deflectors 50 and 50 that serveas air flow control means. The deflectors are movably connected to ductat connections 52 and 52' and are given a synchronized motion by movingmeans 54 and 54'.

FIG. 6 shows the use of a rotating deflector 55 located in a shroud 56as the air flow control means for the right edge of the condenser 26.

The air flow control means should be able to operate at a frequency ofat least cycles (fully open to fully closed to fully open) per yard oftravel of the web, e.g., 250 cycles/minute for web speed of l0yards/minute.

The total area of the two air flow control means through which air flowsshould be at least about 2 percent of the total condenser area exposedto the air stream. As the severity of the streaks and/or speed of webincreases (e.g., from 10 to 50 yards per minute or more) the total areaof controlled air flow should be increased to as much as percent ormore.

In operation, the frequency of operation of the air flow control meansis increased from zero until the streaks have been blended into theadjoining areas of the web and are not apparent. This minimum effectivefrequency can be somewhat further increased but streaks may reappear athigher frequencies.

Other embodiments of air-flow control means include a shutter-likedevice that rotates in a plane parallel to the condenser screen. Thesecan be placed at the edges of the air duct just upstream of thecondenser screen, immediately behind the screen or can be placed behinda conduit in the vacuum duct that has an air seal on its forward edgethat contacts the condenser screen.

EXAMPLE Apparatus of the general type shown in FIG. 1 is used to form aweb weighing about 0.9 oz./yd. at a rate of yards per minute. The feedbatt of 1.25-denier per fiber, 0.75 inch polyester staple, is fed to a16-inch diameter disperser roll rotating at a surface speed of 14,600feet per minute. Air is supplied through the duct at 6,800 feet perminute. The fiber stream is about 63 inches wide and 0.6 inch thick atthe point of contact with the condensing screen. The condensing screenhas an area 1.9 X inches exposed to the air duct. A rotating valve(FIGS. 2 and 4), 4.5 inches long and 3.87 inches in diameter, is locatedbehind both edges of the condenser screen with the inner edges of thevalves being located about 29 inches from the center of the condensingzone as shown in FIG. 3. The total area of the screen opened and closedby the two valves is about 13 percent of the condenser area exposed tothe air stream. Operation of the valves at 500 revolutions per minute(1,000 cycles per minute) effectively blends out streaks.

I claim:

1. In an air-laydown apparatus having duct means for conveying fibers ina controlled flow of air, fiber disperser means for projecting fibersinto the duct means to form a thin stream of fibers in air, air supplymeans for directing a low turbulence flow of air through the duct means,and a moving condenser screen for collecting the fibers thereon to forma web; the improvement for avoiding the formation of web streaks whereinthe improvement comprises air-flow control valves located near oppositeedges of the condenser screen for alternately interrupting air flowthrough the screen on opposite sides of the fiber stream at a frequencyof at least 25 cycles per minute for each yard per minute of screentravel.

2. In an air-laydown apparatus having duct means for conveying fibers ina controlled flow of air, fiber disperser means for projecting fibersinto the duct means to form a thin stream of fibers in air, air supplymeans for directing a low turbulence flow of air through the duct means,and a moving condenser screen for collecting the fibers thereon to forma web; the improvement for avoiding the formation of web streaks,wherein the improvement comprises air-flow control means for alternatelyinterrupting air flow on opposite sides of the fiber streamcharacterized by a pair of rotating drums located behind opposite edgesof the condenser screen and having opposed openings with each openingapproximating the area of intervening closed drum areas.

1. In an air-laydown apparatus having duct means for conveying fibers ina controlled flow of air, fiber disperser means for projecting fibersinto the duct means to form a thin stream of fibers in air, air supplymeans for directing a low turbulence flow of air through the duct means,and a moving condenser screen for collecting the fibers thereon to forma web; the improvement for avoiding the formation of web streaks whereinthe improvement comprises air-flow control valves located near oppositeedges of the condenser screen for alternately interrupting air flowthrough the screen on opposite sides of the fiber stream at a frequencyof at least 25 cycles per minute for each yard per minute of screentravel.
 2. In an air-laydown apparatus having duct means for conveyingfibers in a controlled flow of air, fiber disperser means for projectingfibers into the duct means to form a thin stream of fibers in air, airsupply means for directing a low turbulence flow of air through the ductmeans, and a moving condenser screen for collectIng the fibers thereonto form a web; the improvement for avoiding the formation of webstreaks, wherein the improvement comprises air-flow control means foralternately interrupting air flow on opposite sides of the fiber streamcharacterized by a pair of rotating drums located behind opposite edgesof the condenser screen and having opposed openings with each openingapproximating the area of intervening closed drum areas.